Chain or belt tensioner with a one-way clutch

ABSTRACT

A tensioner comprising a first cylindrical member to be fixedly attached to a stationary portion, a movable eccentric member in the form of a cylinder and eccentrically rotatably provided around the first member, an idler in the form of a hollow cylinder and rotatably provided around the movable eccentric member for contact with a wrapping connector driving member, and a spring provided between the stationary portion and the movable eccentric member for biasing the eccentric member in a direction to press the idler into contact with the wrapping connector driving member. A one-way clutch is provided between the first member and the movable eccentric member.

This is a division, of application Ser. No. 136,312 filed Dec. 22, 1987.

BACKGROUND OF THE INVENTION

The present invention relates ro a tensioner for wrapping connectordriving members, such as belts and chains, and more particularly to atensioner for giving specified tension, for example, to a timing beltreeved around a pulley on the crankshaft of a motor vehicle engine and apulley on the camshaft thereof.

The timing belt is provided with a tensioner including an idler which ispressed against the belt as by the force of a spring to give a specifiedtensioning force to the belt by absorbing the stretch of the belt due tochanges in the temperature of the engine or the elongation of the beltdue to use.

Such belt tensioners heretofore known include one which comprises apivot fixed to an engine or like fixed portion, and an arm rotatablysupported on the pivot, having an idler rotatably mounted on its forwardend and biased by a spring in a direction to press the idler against thebelt (U.S. Pat. No. 4,610,683).

However, the conventional belt tensioner is relatively large-sized,requires a large space for installation and is cumbersome to handlebecause the idler is mounted on the forward end of the arm which ismovable about the pivot.

Such belt tensioners are provided with a hydraulic damper forsuppressing the resonance of the idler due to the vibration of the beltor of the engine. Nevertheless, the belt tensioner equipped with thehydraulic damper permits leakage of the oil, must therefore bereplenished with oil and is cumbersome to maintain. Moreover, thehydraulic damper is complex in construction and expensive.

SUMMARY OF THE INVENTION

The main object of the present invention is to provide a tensioner for abelt, chain or the like which is simple in construction and inexpensive,can be compacted, and is therefore easy to handle and can be installedin a reduced space.

The tensioner of the present invention comprises a solid cylindricalfixed member to be fixedly attached to a stationary portion, a movableeccentric member in the form of a solid cylinder and eccentricallyrotatably provided around the fixed member, an idler in the form of ahollow cylinder and rotatably provided around the movable eccentricmember for contact with a wrapping connector driving member, and aspring provided between the stationary portion and the movable eccentricmember for biasing the eccentric member in a direction to press theidler into contact with the wrapping connector driving member, ahigh-viscosity oil being provided in a clearance between the outerperiphery of the fixed member and the inner periphery of the movableeccentric member.

The tensioner of the present invention can be compacted in its entirety,is easy to handle and can be installed in a small space because themovable eccentric member and the idler are provided around the fixedmember and further because the high-viscosity oil provided between thefixed member and the eccentric member serves a dampening function. Thehigh-viscosity oil, acting to diminish vibration with its viscousresistance, permits the tensioner to exhibit stable performance over aprolonged period of time, whereas the construction wherein the oil isprovided merely in the clearance defined by the outer periphery of thefixed member and the inner periphery of the eccentric member is simple,inexpensive and free of oil leakage, consequently assuring facilitatedmaintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in cross section taken along the line I--I in FIG. 2and showing a belt tensioner as a first embodiment of the invention;

FIG. 2 is a view in longitudinal section taken along the line II--II inFIG. 1;

FIG. 3 is a view of the embodiment as it is seen in the direction ofarrows III--III in FIG. 2;

FIG. 4 is a view in cross section taken along the line IV--IV in FIG. 2;

FIG. 5 is a view in cross section taken along the line V--V in FIG. 6and showing another belt tensioner as a second embodiment of theinvention;

FIG. 6 is a view in longitudinal section taken along the line VI--VI inFIG. 5;

FIG. 7 is a view in cross section taken along the line VII--VII in FIG.6;

FIG. 8 is a view in longitudinal section taken along the line VIII--VIIIin FIG. 9 and showing another belt tensioner as a third embodiment ofthe invention;

FIG. 9 is a view in cross section taken along the line IX--IX in FIG. 8;

FIG. 10 is a view in cross section taken along the line X--X in FIG. 11and showing another belt tensioner as a fourth embodiment of theinvention;

FIG. 11 is a view in longitudinal section taken along the line XI--XI inFIG. 10;

FIG. 12 is a view of the tensioner as it is seen in the direction ofarrows XII--XII in FIG. 11; and

FIG. 13 is a view in cross section taken along the line XIII--XIII inFIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying drawings, the present invention willbe described below as it is embodied for the timing belt for motorvehicle engines.

FIGS. 1 to 4 show a first embodiment.

The belt tensioner of the first embodiment is secured to a stationaryportion (e.g. the cylinder block) 11 of an engine by a fixed rod 10 inthe form of a bolt.

The fixed rod 10 has at its one end a screw portion 10b slightly smallerthan an intermediate solid cylinder portion 10a thereof in outsidediameter and is formed with a flange 10c and a head 10d integrally withthe other end thereof. A side plate 12 in the form of an annular diskand having substantially the same outside diameter as the flange 10c ispress-fitted to the screw portion 10b of the fixed rod 10. The fixed rod10 is secured to the stationary portion 11 with the screw portion 10bscrewed into the portion 11, whereby the side plate 12 is clampedbetween the rod cylinder portion 10a and the stationary portion 11.

A hollow cylindrical intermediate member 13, slightly shorter than thecylinder portion 10a and having a smaller outside diameter than theflange 10c and the side plate 12, is provided around the solid cylinderportion 10a concentrically therewith, with a one-way clutch 14interposed between the cylinder portion 10a and member 13. Theintermediate member 13 has at its one portion toward the flange 10c aninside diameter slightly larger than the outside diameter of thecylinder portion 10a of the fixed rod 10. The other portion of themember 13 has an inside diameter larger than this inside diameter.Adjacent to the side plate 12, a sleeve 15 is inserted in theintermediate member 13 around the cylinder portion 10a. At the middle ofthe rod cylinder portion 10a, the one-way clutch 14 is disposed in anannular space between the cylinder portion 10a and the intermediatemember 13. The one-way clutch 14, which is for example a known one-wayroller clutch, is disengaged when intermediate member 13 rotatescounterclockwise in FIG. 1 relative to the fixed rod 10, permitting thecounterclockwise rotation, but is engaged when the member 13 rotatesclockwise in FIG. 1 to lock the member 13.

A movable eccentric member 16 in the form of a short cylinder having thesame length as the intermediate member 13 is eccentrically rotatablyprovided around the intermediate member 13. The eccentric member 16 hasan eccentric bore 17 having the member 13 fitted therein. The clearancebetween the outer periphery of the intermediate member 13 and the boredefining inner periphery of the eccentric member 16 is minimized.Silicone oil O, for example at least 100000 cst. (25° C.) in viscosity,is provided in the clearance to give an increased rotational torque tothe eccentric member 16. The rotational torque, which is dependent onthe viscosity of the oil O, is determined also according to the outsidediameter and length of the intermediate member 13 and to the size of theclearance between the member 13 and the eccentric member 16. O-rings 18and 19 are interposed between these members 13 and 16 at theirrespective ends for confining the oil in the clearance.

A hollow cylindrical idler 20 provided around the eccentric member 16with a plurality of spherical rolling members 21 interposed therebetweenis rotatable but is almost prevented from moving in the axial direction.

The eccentric member 16 has adjacent to the side plate 12 a boss portion16a substantially concentric with the fixed rod 10. A coiled torsionspring 22 is provided around the boss portion 16a and has one end 22aengaged with a pin 23 fixed to a stepped portion 16c of the eccentricmember 16 which portion 16c is provided between the boss portion and anaccentric portion 16b of the member 16. The other end 22b of the springis engaged with a pin 24 fixed to the stationary portion 11. The spring22 biases the eccentric member 16 counterclockwise in FIG. 1, pressingthe idler 20 against one side of a timing belt 25 opposite to the otherside thereof having teeth 26.

The eccentric portion 16b of the eccentric member 16 is formed with apin insertion bore 27 extending therethrough axially. Before the belttensioner is attached to the engine, a set pin 28 is inserted into thebore 27 from the flange (10c) side. The set pin 28, projecting from thestepped portion 16c of the member 16, is positioned outside the bossportion 16a, and the end 22b of the spring 22 to be engaged with the pin24 on the stationary portion 11 is in engagement with the set pin 28.The spring 22 in this state has its force set to a suitable value.

After the fixed rod 10 and the side plate 12 have been secured to thestationary portion 11 in this state as shown in FIG. 2, the set pin 28is removed from the eccentric member 16. The spring end 22b is engagedwith the pin 24 on the stationary portion 11, whereby the belt tensionercan be installed in place easily.

If the belt 25 abruptly slacks, for example, owing to quick accelerationof the engine, the eccentric member 16 is forced into counterclockwiserotation in FIG. 1 by the action of the spring 22, with the intermediatemember 13 also acting to rotate in the same direction by virtue of theviscous resistance of the oil O. Since the one-way clutch 14 isdisengaged, permitting the rotation of the intermediate member 13 inthis direction, the eccentric member 16 rapidly rotates with theintermediate member 13 in the counterclockwise direction in FIG. 1,causing the idler 20 to quickly follow the slacking of the belt 25 to bepressed against the belt, which in turn is held under tension asspecified. This eliminates the likelihood that some teeth on the belt 25will fail to engage the member concerned. Conversely, when the tensionbuilds up owing to the contraction of the belt 25, the eccentric member16 acts to rotate clockwise in FIG. 1 against the force of the spring22, and the intermediate member 13 also acts to rotate in the samedirection owing to the viscous resistance of the oil O. However, theone-way clutch 14 engages to prevent the rotation of the intermediatemember 13 in this direction, so that the eccentric member 16 only gentlyrotates clockwise in FIG. 1 against the viscous resistance of the oil O,slowly shifting the idler 20 until the tension on the belt 25 lowers tothe specified value. The vibration of the idler 20 due to the vibrationof the belt 25 and the vibration of the engine is diminished by theviscous resistance of the silicone oil O acting against the rotation.

Thus, the viscous resistance of the silicone oil exhibits a dampeningeffect, assuring the tensioner of stable performance over a prolongedperiod of time without the need of oil replenishment. The tensioner isvery simple and compact in construction and inexpensive, and can beinstalled in a small space.

The silicone oil O can be provided in the clearance between theintermediate member 13 and the eccentric member 16 by applying the oilto one or both of the outer periphery of the intermediate member 13 andthe inner periphery of the eccentric member 16 an thereafter fittingthese members to each other. The silicone oil can be spread throughoutthe entire clearance easily also by forming a helical small groove oraxial small grooves in the outer periphery of the intermediate member 13or in the bore defining inner periphery of the eccentric member 16,placing the oil into the groove(s) and thereafter rotating the eccentricmember 16 as fitted around the intermediate member 13. It is alsopossible to cause the outer periphery of the intermediate member 13 orthe inner periphery of the eccentric member 16 to retain the siliconeoil in an annular groove formed therein.

In the case of the above belt tensioner, the screw portion 10b of thefixed rod 10 is right-handed, and the direction in which the screwportion 10b is tightened up agrees with the direction (clockwise inFIG. 1) of rotation of the eccentric member 16 when the tension on thebelt 25 builds up. Consequently, when the belt tension increases, theone-way clutch 14 engages as already stated, subjecting the fixed rod 10to a torque acting to further tightening the rod. Conversely, when thetension on the belt 25 diminishes, the one-way clutch 14 is disengaged,rendering the rod 10 free of the torque acting to loosen the rod. Thus,there is no likelihood that the fixed rod 10 will loosen during use.Further because the clutch 14 is engaged by rotating the eccentricmember 16 and the intermediate member 13 in the direction to tighten thefixed rod 10 while the rod 10 is held in fixed state, the clutch 14 isdisengaged by rotating the fixed rod 10 in the tightening direction,with the eccentric member 16 and the intermediate member 13 held infixed state. Accordingly, the tensioner can be installed in place easilyby rotating the fixed rod 10 only in the tightening direction.

FIGS. 5 to 7 show a second embodiment.

A stepped fixed rod 31 is secured at its base end 31a to a stationaryportion 30 of an engine. A hollow cylindrical intermediate member 33 isprovided around an intermediate solid cylinder portion 31b of the fixedrod 31, with a one-way clutch 32 interposed therebetween. Like theclutch 14 of the first embodiment, the clutch 32 permits theintermediate member 33 to rotate counterclockwise in FIG. 5 relative tothe fixed rod 31 but prevents clockwise rotation in FIG. 5 of the member33. An eccentric member 34 in the form of a short cylinder iseccentrically rotatably provided around the intermediate member 33. Themember 33 is fitted in an eccentric bore 35 in the eccentric member 34.As in the case of the first embodiment, silicone oil O is provided in aclearance between the outer periphery of the intermediate member 33 andthe inner periphery defining the eccentric bore 35 of the member 34.Side plates 36 and 37 each in the form of an annular disk are secured tothe respective end faces of the intermediate member 33 concentricallytherewith. The side plates 36, 37 have an inside diameter slightlylarger than the outside diameter of the intermediate cylinder portion31b of the rod 31 and are greater than the intermediate member 33 inoutside diameter. The eccentric member 34 is equal to the intermediatemember 33 in length. The opposite end face portions of the eccentricmember 34 close to its inner periphery are in contact with the innersurface portions of the respective side plates 36, 37 close to theirouter peripheries. O-rings 38, 39, 40, 41 for confining the oil O arefitted in the opposite end faces of the intermediate member 33 and ofthe eccentric member 34, in pressing contact with the side plates 36,37. As in the case of the first embodiment, a hollow cylindrical idler42 is provided around the eccentric member 34, with a plurality ofspherical rolling members 43 interposed therebetween. The idler 42 isrotatable but is almost prevented from axial movement. A collar 44 isfitted to a stepped portion between the intermediate cylinder portion31b of the rod 31 and a screw portion 31c thereof at its top end and isfastened by a nut 45 screwed on the screw portion 31c. The side plates36, 37 are held at their inner peripheral portions between the collar 44and a stepped portion between the cylinder portion 31b of the rod 31 andthe base end 31a thereof, whereby the overall assembly is held almostimmovable axially thereof. A coiled torsion spring 46 is fitted aroundthe base end portion 31a of the fixed rod 31 and has its opposite ends46a, 46b anchored in the eccentric member 34 and the stationary portion30, respectively. The spring 46 biases the eccentric member 34counter-clockwise in FIG. 5, pressing the idler 42 against one side of atiming belt 47 opposite to the other side thereof having teeth 48.

The belt tensioner of the second embodiment operates in the same manneras the first.

FIGS. 8 and 9 show a third embodiment.

Two fixed members 51, 52, each in the form of a stepped cylinder, areconcentrically secured to a stationary portion 50 of an engine by afixed rod 53 in the form of a bolt. The first of the fixed members, 51,has a flange 51a at one end thereof adjacent to the stationary portion50, and a small-diameter portion 51c toward the other end thereof.Between the flange 51a and the small-diameter portion 51c, the fixedmember 51 has an intermediate member support portion 51b having anintermediate outside diameter between the outside diameters of theflange and the portion 51c. The small-diameter portion 51c extendstoward the head end of the fixed rod 53 and is fitted in the secondfixed member 52. The second fixed member 52 has a flange 52a at one endthereof adjacent to the head end of the fixed rod 53. The remainingportion of the member 52 serves as an intermediate member supportportion 52b having the same diameter as the support portion 51b of thefirst fixed member 51. Formed around the small-diameter portion 51c ofthe first fixed member 51 is an annular groove 54 between the supportportions 51b, 52b of the two fixed members 51, 52. An intermediatemember 55 in the form of a hollow cylinder having a smaller outsidediameter than the flanges 51a, 52a is provided around the supportportions 51b, 52b concentrically therewith. As is the case with thefirst embodiment, one-way clutch 56 is disposed in the annular groove 54for permitting the intermediate member 55 to rotate clockwise in FIG. 9relative to the fixed members 51, 52 but preventing the rotation thereofin the opposite direction. A movable eccentric member 57 in the form ofa short cylinder is eccentrically rotatably fitted around theintermediate member 55. Silicone oil 0 is provided in a clearancebetween the outer periphery of the intermediate member 55 and the innerperiphery of the eccentric member 57 defining its eccentric bore 58.O-rings 59, 60 for confining the oil ) are interposed between theintermediate member 55 and the eccentric member 57 at their oppositeends. A hollow cylindrical idler 61 is provided around the eccentricmember 57 with a plurality of spherical rolling members 62 interposedtherebetween. The eccentric member 57 has, at one end thereof close tothe stationary portion 50, a boss portion 57a carrying a coiled torsionspring 63 therearound. The spring 63 has one end 63a in engagement witha first pin 64 anchored in a stepped portion 57c of the eccentric member57 and the other end 63b engaged with a pin 65 fixed in the stationaryportion 50. The spring 63 is bent at a portion thereof close to the end63a, and the bent portion 63c is engaged with a second pin 66 anchoredin the stepped portion 57c of the eccentric member 57, on one side ofthe pin 66 opposite to the side where the end 63ais engaged with thefirst pin 64, the second pin 66 thus being adapted to bear the reactionto be exerted by the first pin 64. The spring 63 biases the eccentricmember 57 clockwise in FIG. 9 to press the idler 61 against a timingbelt 69.

In the absence of the second pin 66, the reaction from the first pinwould press the spring 63 against the boss portion 57a of the eccentricmember 57, possibly impeding smooth rotation of the eccentric member 57,whereas in the case of the present embodiment, the second pin 66 bearsthe reaction from the first pin 64, obviating the likelihood that thespring 63 will be pressed against the boss portion 57a and consequentlyassuring the eccentric member 57 of smooth rotation.

Before the belt tensioner is attached to the engine, a set pin 68 isinserted through a bore 67 through the eccentric portion 57b of theeccentric member 57, and the spring end 63b to be engaged with the pin65 on the stationary portion 50 is engaged with the set pin 68 as in thefirst embodiment.

The belt tensioner of the third embodiment is assembled and operates inthe same manner as in the case of the first embodiment.

With the foregoing three embodiments, the intermediate member isprovided around the fixed rod with one-way interposed therebetween, andthe movable eccentric member is fitted around the intermediate memberwith silicone oil provided therebetween. Alternatively, the movableeccentric member may be fitted around the fixed rod or a cylindricalmember fixedly provided around the fixed rod, with silicone oil providedon the inner periphery of the eccentric member.

FIGS. 10 to 13 show such an embodiment, i.e. a fourth embodiment.

A solid cylindrical fixed member 71 and side plates 72, 73 attached tothe respective ends of the member 71 and each in the form of an annulardisk are concentrically secured to a stationary portion 70 of an engineby a fixed rod 74 in the form of a bolt. A movable eccentric member 75in the form of a short cylinder is eccentrically rotatably fitted aroundthe fixed member 71. Silicone oil 0 is provided in a clearance betweenthe outer periphery of the fixed member 71 and the inner surface of theeccentric member 75 defining an eccentric bore 76. Seals 77, 78 forconfining the oil O is provided between the fixed member 71 and theeccentric member 75 at their respective opposite ends. A hollowcylindrical idler 79 is provided around the eccentric member 75, with aplurality of spherical rolling members 80 disposed therebetween. Theeccentric member 75 has a boss portion 75a closer to the stationaryportion 70 and carrying a coiled torsion spring 81 therearound. Thespring 81 has one end 81a engaged with a first pin 82 anchored in astepped portion 75c of the 81a and engaged with a second pin 83 fixed tothe stepped portion 75c, and the other end 81b engaged with a pin 84fixed in the stationary portion 70. The spring 81 biases the eccentricmember 75 counterclockwise in FIG. 10, pressing the idler 79 against atiming belt 89.

The side plate 73 adjacent to the head end of the fixed rod 74 has alarge-diameter portion 73a over about one-half of its circumference anda small-diameter portion 73b corresponding to the remaining approximateone-half of the circumference. A restricting pin 85 is fixed to the endface of an eccentric portion 75b of the member 75 and is positionedoutwardly of the small-diameter diameter portion 73b but inwardly of thelarge-diameter portion 73a. The range of rotation of the eccentricmember 75 is restricted by the contact of the pin 85 with thelarge-diameter portion 73a. A semicircular cutout 86 is formed in theouter peripheral edge of the large-diameter portion 73a of the sideplate 73, while a pin insertion bore 87 corresponding to the cutout 86extends through the eccentric portion 75b of the member 75.

Before the belt tensioner is attached to the engine, a set pin 88 isfitted in the cutout 86 of the side plate 73 and inserted through thebore 87 of the eccentric member 75, and the end 81b of the spring 81 tobe engaged with the pin 84 on the stationary portion 70 is engaged withthe set pin 88.

The belt tensioner of the fourth embodiment is similar to the thirdembodiment in its assembling procedure and operation except that it hasno one-way clutch.

The tensioners of the invention are of course usable for belts andchains other than the timing belts for motor vehicle engines.

What is claimed is:
 1. A tensioner comprising a first cylindrical memberto be fixedly attached to a stationary portion, a movable eccentricmember in the form of a cylinder and eccentrically provided around thefirst member with a one-way clutch interposed therebetween, an idler inthe form of a hollow cylinder and rotatably provided around the movableeccentric member for contact with a wrapping connector driving member,and a spring provided between the stationary portion and the movableeccentric member for biasing the eccentric member in a direction topress the idler into contact with the wrapping connector driving member,the one-way clutch permitting the eccentric member to rotate in adirection to press the idler against the wrapping connector drivingmember but preventing the eccentric member from rotating in a directionto move the idler from the wrapping connector driving member.
 2. Atensioner as defined in claim 1, wherein the movable eccentric memberincludes a cylindrical intermediate member mounted by a one-way clutchon the outer periphery of the first cylindrical member and a cylindricalexternal eccentric member attached eccentrically and rotatably on theoutside of the intermediate member, a vibration absorbing means beinginterposed between the external eccentric member and the intermediatemember so as to absorb the vibration of the wrapping connector drivingmember, a spring to bias the idler in such a direction to press theidler into contact with the wrapping connector driving member beingprovided between the stationary portion and the external eccentricmember.
 3. A tensioner as defined in claim 2, wherein the vibrationabsorbing means is a high viscosity oil interposed between the outerperiphery of the intermediate member and the inner periphery of theexternal eccentric member.